The present invention relates to a switched-capacitor-type stabilized power circuit in which switching elements are respectively provided before and after a capacitor so as to carry out step-up operation by switching a connection of the capacitor and an inputted direct-current power source between series and parallel, and in particular to a switched-capacitor-type stabilized power circuit using batteries as the inputted direct-current power source.
FIG. 5 is a block diagram showing an electrical arrangement of a typical switched-capacitor-type stabilized power circuit 1 adopting a conventional technique. The switched-capacitor-type stabilized power circuit 1 generally has an arrangement such that a step-up capacitor c1, an input smoothing capacitor c2, an output smoothing capacitor c3 and voltage-dividing resistors r1 and r2 for an outputted voltage feedback are externally provided to a control circuit chip 2.
The step-up capacitor in the switched-capacitor-type stabilized power circuit 1 has a single stage arrangement denoted by a reference code cl. In the control circuit chip 2, a pair of switches s1 and s2 is provided before the capacitor c1, and a pair of switches s3 and s4 is provided after the capacitor c1. The control circuit 3 turns on/off the pair of switches s1 and s2 at the same time, and turns on/off the pair of switches s3 and s4 at the same time. Further, the control circuit 3 makes the pair of switches s1 and s2, and the pair of switches s3 and s4 to carry out a reverse operation each other (the pair of switches s1 and s2 is on when the pair of switches s3 and s4 is off, and the pair of switches s1 and s2 is off, when the pair of switches s3 and s4 is on.)
In a charge-period, the pair of switches s1 and s2 is on, and an inputted direct-current voltage vin from a battery is applied to the capacitor c1 after being smoothed by the capacitor c2. Thus, the capacitor c1 is charged with the inputted direct-current voltage vin. In a discharge period, the pair of switches s3 and s4 is on, and the inputted direct-current voltage vin and a charged voltage of the capacitor c1 are joined together. Therefore, a voltage of 2xc3x97vin is supplied to the capacitor c3. This voltage is smoothed by the capacitor c3, and is outputted as an outputted voltage vo. In this manner, a step-up operation to double the voltage is carried out.
The output voltage vo becomes a feedback voltage vadj after being divided by the voltage-dividing resistors r1 and r2, and is compared to a reference voltage vref from a reference voltage source 4 by a hysteresis comparator 5, and a result of the comparison is inputted to the control circuit 3. The control circuit 3 makes the pair of switches s1 and s2 and the pair of switches s3 and s4 to carry out the switching operation until the feedback voltage vadj reaches to the reference voltage vref, and makes the pair of switches s1 and s2 and the pair of switches s3 and s4 to stop the operation when the feedback voltage vadj reaches to the reference voltage vref. As described, the outputted voltage vo stays constant regardless of a load.
In the stabilized power circuit 1 having the foregoing arrangement, the inputted direct-current voltage vin is supplied from a constant voltage circuit 6 as a power source to the control circuit 3, and also to the hysteresis comparator 5 which control the switching operation. Accordingly, in the case of the input from a battery, when the voltage of the battery decreases to a voltage smaller than the operation voltage of the control circuit 3 or the like, the control operation does not work properly, and the outputted voltage vo decreases due to an increase of on-state resistance of the switching elements which are included in the switches s1, s2, s3 and s4.
The present invention is made to provide a switched-capacitor-type stabilized power circuit capable of carrying out a proper step-up operation even when an inputted direct-current decreases.
In order to solve the foregoing problems, the switched-capacitor-type stabilized power circuit of the present invention includes;
switching elements provided before and after a capacitor;
a control section which controls the switching elements, for switching a connection of the capacitor and an inputted direct-current power source between series and parallel, so as to carry out step-up operation;
a feedback comparator which gives feedback of information relating to an outputted voltage to the control section, so as to stabilize the outputted voltage;
a constant voltage circuit which supplies power to the control section; and
switching means for selecting an inputted direct-current voltage at rising of the inputted direct-current voltage, and selecting an outputted voltage after the rising of the outputted voltage, for a voltage supplied to the constant voltage circuit in response to the feedback comparator.
With the foregoing arrangement, the switched-capacitor-type stabilized power circuit selects the inputted direct-current voltage at rising of the inputted direct-current voltage and selects the outputted voltage after the rising of the outputted voltage for the voltage supplied to the constant voltage circuit which supplies power to the control section by using a signal from the feedback comparator which gives feedback of information relating to the outputted voltage to the control section so as to stabilize the outputted voltage.
Accordingly, once the step-up operation is carried out in a state where the inputted direct-current voltage is at or greater than the operation voltage of the control section, it is possible to maintain a proper operation even when the inputted direct-current voltage decreases. Further, a signal of the hysteresis comparator is used for the switching for an input of the constant voltage circuit which supplies the power source to the control section. Thus, the circuit can be simplified.
Further, in order to solve the foregoing problems, the switched-capacitor-type stabilized power circuit of the present invention includes;
switching elements provided before and after a capacitor;
a control section which controls the switching elements, for switching a connection of the capacitor and an inputted direct-current power source between series and parallel, so as to carry out step-up operation;
a constant voltage circuit which supplies power to the control section; and
switching means for selecting the inputted direct-current voltage at rising of the inputted direct-current voltage and selecting the outputted voltage after the rising of the outputted voltage and selecting a off-state when the outputted voltage is higher than a predetermined level, for the voltage supplied to the constant voltage circuit.
With the foregoing arrangement, the switched-capacitor-type stabilized power circuit selects the inputted direct-current voltage at rising of the inputted direct-current voltage and selecting the outputted voltage after the rising of the outputted voltage and selecting the off-state when the outputted voltage is higher than the predetermined level, for the voltage supplied to the constant voltage circuit which supplies power to the control section.
Accordingly, once the step-up operation is carried out in a state where the inputted direct-current voltage is at or greater than the operation voltage of the control section, it is possible to maintain a proper operation even when the inputted direct-current voltage decreases. Further, under light-load condition and when the outputted voltage is higher than the predetermined level, there will be no troubles if the step-up operation by the switched-capacitor stops. Thus, in that condition, the power supply to the constant voltage circuit is cut off, and the operation of the control section is stopped. Therefore, power consumption can be reduced.
Further, a step-up circuit may be provided for carrying out the step-up operation with respect to the voltage supplied to the constant voltage circuit at the rising of the inputted direct-current voltage.
With the foregoing arrangement, even in the state where the inputted direct-current voltage is at or smaller than the operation voltage of the control section, it is possible to supply a voltage at or greater than the operation voltage of the control section. Thus, a proper operation can be carried out even in the state where the inputted direct-current voltage is at or smaller than the operation voltage of the control section.
Further, in addition to the foregoing arrangement, step-up stopping means may be provided for cutting off the voltage supplied to the constant voltage circuit after the rising of the outputted voltage.
With the foregoing arrangement, it is possible to stop unnecessary operation of the step-up circuit, and power consumption can be reduced.
Furthermore, in addition to the foregoing arrangement, the step-up stopping means may be the feedback comparator which gives feedback of the outputted voltage to the control section so as to stabilize the outputted voltage.
with the foregoing arrangement, the circuit can be simplified since the feedback comparator works as the step-up stopping means.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.